Virtual operating system device communication relying on memory access violations

ABSTRACT

Attempts by drivers of a virtualized legacy computer game to communicate with nonexistent legacy game system hardware are converted into calls to actual hardware of the host computer game system. An access control list (ACL) restricting and/or reducing page permissions is used to explicitly forbid the drivers of the legacy computer game operating on the virtualized legacy computer game platform from writing to the MMIO addresses of the legacy computer game system. When the operating system of the virtualized legacy computer game platform attempts to touch its driver memory by writing to the MMIO addresses, the operating system of the host computer game system perceives a memory access violation, suspends the virtual machine implementing the virtualized computer game platform, and passes the intended write to an exception handler of the host operating system. The exception handler of the host operating system translates the attempted hardware access command into the command language of the host operating system and then returns control to the operating system of the virtualized legacy computer game platform. The legacy game is completely unaware of this address translation in that it sees only a successful hardware result and proceeds.

FIELD OF THE INVENTION

The invention is directed to systems and methods for virtualizinghardware devices in a virtual machine (VM) environment and, moreparticularly, the invention is directed to systems and methods for usingmemory access violations to instruct the host system to perform anaddress translation to enable access to actual memory mapped hardwaredevices of the host system.

BACKGROUND OF THE INVENTION

When updating hardware architectures of computer systems such as gameconsoles to implement faster, more feature rich hardware, developers arefaced with the issue of backwards compatibility to the legacy computersystem for application programs or games developed for the legacycomputer system platform. In particular, it is commercially desirablethat the updated hardware architecture support application programs orgames developed for the legacy hardware architecture. However, if theupdated hardware architecture differs substantially, or radically, fromthat of the legacy hardware architecture, architectural differencesbetween the two systems may make it very difficult, or even impossible,for legacy application programs or games to operate on the new hardwarearchitecture without substantial hardware modification and/or softwarepatches. Since customers generally expect such backwards compatibility,a solution to these problems is critical to the success of the updatedhardware architecture.

Recent advances in PC architecture and software emulation have providedhardware architectures for computers, even game consoles, that arepowerful enough to enable the emulation of legacy application programsor games in software rather than hardware. Such software emulatorstranslate the title instructions for the application program or game onthe fly into device instructions understandable by the new hardwarearchitecture. This software emulation approach is particularly usefulfor backwards compatibility for computer game consoles since thedeveloper of the game console maintains control over both the hardwareand software platforms and is quite familiar with the legacy games.

However, to enable emulation of the host hardware, computer gamesystems, such as Xbox, pose a particular problem. Unlike an operatingsystem (OS) of a personal computer (PC), the operating system of acomputer game system is generally not stored entirely within the consoleof the computer game system itself. Instead, many of the drivers andmiddleware layers are shipped on each and every game disc and staticallylinked in to ensure perfect compatibility between the game and thecomputer game system software. Unfortunately, this means that when thecomputer game platform for a legacy computer game system is virtualizedusing software emulation, the legacy games will continue to attempt tocommunicate with non-existent legacy computer game system hardware. Forexample, in the legacy Xbox computer game system, drivers from the gamediscs communicate with hardware devices by writing to memory-mappeddevice I/O (MMIO) addresses. However, once the legacy Xbox computer gamesystem is virtualized using software emulation, these MMIO addresses aremeaningless.

Accordingly, a technique is needed to enable the legacy computer gamesdrivers to communicate with the hardware of the new host game systemeven when the legacy computer game system is virtualized using softwareemulation. The present invention addresses this need in the art.

SUMMARY OF THE INVENTION

The invention addressed the above-mentioned need in the art byconverting attempts by drivers of a legacy computer game to communicatewith the nonexistent legacy game system hardware into calls to actualhardware of the host computer game system. In accordance with theinvention, an access control list (ACL) restricting and/or reducing pagepermissions (e.g. to read only) is used to explicitly forbid the driversof the legacy computer game operating on the virtualized legacy computergame platform from writing to the MMIO addresses of the legacy computergame system. When the operating system of the virtualized legacycomputer game platform attempts to touch its driver memory by writing tothe MMIO addresses, the operating system of the host computer gamesystem perceives a memory access violation, suspends the virtual machineimplementing the virtualized computer game platform, and passes theintended write to an exception handler of the host operating system. Theexception handler of the host operating system passes control to anemulator that translates the attempted hardware access command into thecommand language of the host operating system and performs theoperation. The emulator exits and returns the translation results andcontrol to the operating system of the virtualized legacy computer gameplatform. The legacy game is completely unaware of this addresstranslation in that it sees only a successful hardware result andproceeds.

Those skilled in the art will appreciate that, while an exemplaryembodiment of the invention is implemented in the Xbox computer gamesystem available from Microsoft Corporation, any computer game consoleor other type of computer system in which a substantial part of theoperating system or its drivers are provided on the game media orapplication program media could benefit from the memory access violationapproach to device emulation used in accordance with the invention.Additional characteristics of the invention will be apparent to thoseskilled in the art based on the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The systems and methods for converting attempts by drivers of a legacycomputer game to communicate with the nonexistent legacy game systemhardware into calls to actual hardware of the host computer game systemin accordance with the invention are further described with reference tothe accompanying drawings, in which:

FIG. 1A is a block diagram representing the logical layering of thehardware and software architecture for an emulated operating environmentin a computer system;

FIG. 1B is a block diagram representing a virtualized computing systemwherein the emulation is performed by the host operating system (eitherdirectly or via a hypervisor);

FIG. 1C is a block diagram representing an alternative virtualizedcomputing system wherein the emulation is performed by a virtual machinemonitor running side-by-side with a host operating system;

FIG. 2 illustrates the relationship between the virtual memory of thelegacy game system implemented in a virtual machine and the virtualmemory of the host game system.

FIG. 3 illustrates a system for converting attempts by the virtualizedlegacy game system to communicate with hardware devices into the actualmemory addresses of the hardware of the host game system.

FIG. 4 illustrates a sample embodiment of the invention for enabling thevirtualized legacy game system to access IDE controller hardware of thehost game system.

FIG. 5A is a block diagram representing an exemplary network environmenthaving a variety of computing devices in which the invention may beimplemented; and

FIG. 5B is a block diagram representing an exemplary non-limiting hostcomputing device in which the invention may be implemented.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Overview

The invention converts attempts by drivers of a legacy computer game tocommunicate with the legacy game system hardware into calls to actualhardware of the host computer game system by using an access controllist (ACL) to restrict and/or reduce page permissions (e.g., to readonly) so as to explicitly forbid the drivers of the legacy computer gameoperating on the virtualized legacy computer game platform from writingto the MMIO addresses of the legacy computer game system. Then, when theoperating system of the virtualized legacy computer game platformattempts to touch its driver memory by writing to the MMIO addresses,the operating system of the host computer game system perceives a memoryaccess violation, suspends the virtual machine implementing thevirtualized computer game platform, and passes the intended write to anexception handler of the host operating system. The exception handler ofthe host operating system passes control to an emulator that translatesthe attempted hardware access command into the command language of thehost operating system and performs the operation. The emulator exits andreturns the translation results and control to the operating system ofthe virtualized legacy computer game platform. The legacy game iscompletely unaware of this address translation in that it sees only asuccessful hardware result and proceeds.

Other more detailed aspects of the invention are described below, butfirst, the following description provides a general overview of and somecommon vocabulary for virtual machines, emulators, and associatedterminology as the terms have come to be known in connection withoperating systems and host processor (“CPU”) virtualization techniques.In doing so, a set of vocabulary is set forth that one of ordinary skillin the art may find useful for the description that follows of theapparatus, systems and methods for providing virtual operating systemdevice communication using memory access violations in accordance withthe techniques of the invention.

Overview of Virtual Machines

Computers include general purpose central processing units (CPUs) or“processors” that are designed to execute a specific set of systeminstructions. A group of processors that have similar architecture ordesign specifications may be considered to be members of the sameprocessor family. Examples of current processor families include theMotorola 680X0 processor family, manufactured by International BusinessMachines (IBM) or Motorola, Inc. of Phoenix, Ariz.; the Intel 80X86processor family, manufactured by Intel Corporation of Sunnyvale,Calif.; and the PowerPC processor family, which is manufactured byMotorola, Inc. and used in computers manufactured by Apple Computer,Inc. of Cupertino, Calif. Although a group of processors may be in thesame family because of their similar architecture and designconsiderations, processors may vary widely within a family according totheir clock speed and other performance parameters.

Each family of microprocessors executes instructions that are unique tothe processor family. The collective set of instructions that aprocessor or family of processors can execute is known as theprocessor's instruction set. As an example, the instruction set used bythe Intel 80X86 processor family is incompatible with the instructionset used by the PowerPC processor family. The Intel 80X86 instructionset is based on the Complex Instruction Set Computer (CISC) format,while the Motorola PowerPC instruction set is based on the ReducedInstruction Set Computer (RISC) format. CISC processors use a largenumber of instructions, some of which can perform rather complicatedfunctions, but which generally require many clock cycles to execute.RISC processors, on the other hand, use a smaller number of availableinstructions to perform a simpler set of functions that are executed ata much higher rate.

The uniqueness of the processor family among computer systems alsotypically results in incompatibility among the other elements ofhardware architecture of the computer systems. A computer systemmanufactured with a processor from the Intel 80X86 processor family willhave a hardware architecture that is different from the hardwarearchitecture of a computer system manufactured with a processor from thePowerPC processor family. Because of the uniqueness of the processorinstruction set and a computer system's hardware architecture,application software programs are typically written to run on aparticular computer system running a particular operating system.

Generally speaking, computer manufacturers try to maximize their marketshare by having more rather than fewer applications run on themicroprocessor family associated with the computer manufacturers'product line. To expand the number of operating systems and applicationprograms that can run on a computer system, a field of technology hasdeveloped in which a given computer having one type of CPU, called ahost, will include a virtualizer program that allows the host computerto emulate the instructions of an unrelated type of CPU, called a guest.Thus, the host computer will execute an application that will cause oneor more host instructions to be called in response to a given guestinstruction, and in this way the host computer can both run softwaredesigned for its own hardware architecture and software written forcomputers having an unrelated hardware architecture.

As a more specific example, a computer system manufactured by AppleComputer, for example, may run operating systems and programs writtenfor PC-based computer systems. It may also be possible to usevirtualizer programs to execute concurrently on a single CPU multipleincompatible operating systems. In this latter arrangement, althougheach operating system is incompatible with the other, virtualizerprograms can host each of the several operating systems and therebyallowing the otherwise incompatible operating systems to runconcurrently on the same host computer system.

When a guest computer system is emulated on a host computer system, theguest computer system is said to be a “virtual machine” as the guestcomputer system only exists in the host computer system as a puresoftware representation of the operation of one specific hardwarearchitecture. Thus, an operating system running inside virtual machinesoftware such as Microsoft's Virtual PC may be referred to as a “guest”and/or a “virtual machine,” while the operating system running thevirtual machine software may be referred to as the “host.” Similarly,the operating system in a legacy game system running inside virtualmachine or emulation software inside a new game system may be referredto as the “guest,” while the operating system of the new game systemrunning the virtual machine or emulation software may be referred to asthe “host.” The terms virtualizer, emulator, direct-executor, virtualmachine, and processor emulation are sometimes used interchangeably todenote the ability to mimic or emulate the hardware architecture of anentire computer system using one or several approaches known andappreciated by those of skill in the art. Moreover, all uses of the term“emulation” in any form is intended to convey this broad meaning and isnot intended to distinguish between instruction execution concepts ofemulation versus direct-execution of operating system instructions inthe virtual machine. Thus, for example, Virtual PC software availablefrom Microsoft Corporation “emulates” (by instruction executionemulation and/or direct execution) an entire computer that includes anIntel 80X86 Pentium processor and various motherboard components andcards, and the operation of these components is “emulated” in thevirtual machine that is being run on the host machine. A virtualizerprogram executing on the operating system software and hardwarearchitecture of the host computer, such as a computer system having aPowerPC processor, mimics the operation of the entire guest computersystem.

The general case of virtualization allows one processor architecture torun OSes and programs from other processor architectures (e.g., PowerPCMac programs on x86 Windows, and vice versa), but an important specialcase is when the underlying processor architectures are the same (runvarious versions of x86 Linux or different versions of x86 Windows onx86). In this latter case, there is the potential to execute the GuestOS and its applications more efficiently since the underlyinginstruction set is the same. In such a case, the guest instructions areallowed to execute directly on the processor without losing control orleaving the system open to attack (i.e., the Guest OS is sandboxed).This is where the separation of privileged versus non-privileged and thetechniques for controlling access to memory comes into play. Forvirtualization where there is an architectural mismatch (PowerPC⇄x86),two approaches could be used: instruction-by-instruction emulation(relatively slow) or translation from the guest instruction set to thenative instruction set (more efficient, but uses the translation step).If instruction emulation is used, then it is relatively easy to make theenvironment robust; however, if translation is used, then it maps backto the special case where the processor architectures are the same.

In accordance with the invention, the guest operating system isvirtualized and thus an exemplary scenario in accordance with theinvention would be emulation of a Windows95®, Windows98®, Windows 3.1,or Windows NT 4.0 operating system on a Virtual Server or an Xboxoperating system on an Xbox game console available from MicrosoftCorporation. In various embodiments, the invention thus describessystems and methods for controlling guest access to some or all of theunderlying physical resources (memory, devices, etc.) of the hostcomputer.

The virtualizer program acts as the interchange between the hardwarearchitecture of the host machine and the instructions transmitted by thesoftware (e.g., operating systems, applications, etc.) running withinthe emulated environment. This virtualizer program may be a hostoperating system (HOS), which is an operating system running directly onthe physical computer hardware (and which may comprise a hypervisor).Alternately, the emulated environment might also be a virtual machinemonitor (VMM) which is a software layer that runs directly above thehardware, perhaps running side-by-side and working in conjunction withthe host operating system, and which can virtualize all the resources ofthe host machine (as well as certain virtual resources) by exposinginterfaces that are the same as the hardware the VMM is virtualizing.This virtualization enables the virtualizer (as well as the hostcomputer system itself) to go unnoticed by operating system layersrunning above it.

Processor emulation thus enables a guest operating system to execute ona virtual machine created by a virtualizer running on a host computersystem comprising both physical hardware and a host operating system.

From a conceptual perspective, computer systems generally comprise oneor more layers of software running on a foundational layer of hardware.This layering is done for reasons of abstraction. By defining theinterface for a given layer of software, that layer can be implementeddifferently by other layers above it. In a well-designed computersystem, each layer only knows about (and only relies upon) the immediatelayer beneath it. This allows a layer or a “stack” (multiple adjoininglayers) to be replaced without negatively impacting the layers abovesaid layer or stack. For example, software applications (upper layers)typically rely on lower levels of the operating system (lower layers) towrite files to some form of permanent storage, and these applications donot need to understand the difference between writing data to a floppydisk, a hard drive, or a network folder. If this lower layer is replacedwith new operating system components for writing files, the operation ofthe upper layer software applications remains unaffected.

The flexibility of layered software allows a virtual machine (VM) topresent a virtual hardware layer that is in fact another software layer.In this way, a VM can create the illusion for the software layers aboveit that the software layers are running on their own private computersystem, and thus VMs can allow multiple “guest systems” to runconcurrently on a single “host system.” This level of abstraction isrepresented by the illustration of FIG. 1A.

FIG. 1A is a diagram representing the logical layering of the hardwareand software architecture for an emulated operating environment in acomputer system. In the figure, an emulation program 54 runs directly orindirectly on the physical hardware architecture 52. Emulation program54 may be (a) a virtual machine monitor that runs alongside a hostoperating system, (b) a specialized host operating system having nativeemulation capabilities, or (c) a host operating system with a hypervisorcomponent wherein the hypervisor component performs the emulation.Emulation program 54 emulates a guest hardware architecture 56 (shown asbroken lines to illustrate the fact that this component is the “virtualmachine,” that is, hardware that does not actually exist but is insteademulated by said emulation program 54). A guest operating system 58executes on the guest hardware architecture 56, and software application60 runs on the guest operating system 58. In the emulated operatingenvironment of FIG. 1A—and because of the operation of emulation program54—software application 60 may run in computer system 50 even ifsoftware application 60 is designed to run on an operating system thatis generally incompatible with the host operating system and hardwarearchitecture 52.

FIG. 1B illustrates a virtualized computing system comprising a hostoperating system software layer 64 running directly above physicalcomputer hardware 62 where the host operating system (host OS) 64provides access to the resources of the physical computer hardware 62 byexposing interfaces that are the same as the hardware the host OS isemulating (or “virtualizing”)—which, in turn, enables the host OS 64 togo unnoticed by operating system layers running above it. Again, toperform the emulation the host OS 64 may be a specially designedoperating system with native emulations capabilities or, alternately, itmay be a standard operating system with an incorporated hypervisorcomponent for performing the emulation (not shown).

As shown in FIG. 1B, above the host OS 64 are two virtual machine (VM)implementations, VM A 66, which may be, for example, a virtualized Intel386 processor, and VM B 68, which may be, for example, a virtualizedversion of one of the Motorola 680X0 family of processors. Above each VM66 and 68 are guest operating systems (guest OSes) A 70 and B 72respectively. Running above guest OS A 70 are two applications,application A1 74 and application A2 76, and running above guest OS B 72is application B1 78.

In regard to FIG. 1B, it is important to note that VM A 66 and VM B 68(which are shown in broken lines) are virtualized computer hardwarerepresentations that exist only as software constructions and which aremade possible due to the execution of specialized emulation software(s)that not only presents VM A 66 and VM B 68 to Guest OS A 70 and Guest OSB 72 respectively, but which also performs all of the software stepsnecessary for Guest OS A 70 and Guest OS B 72 to indirectly interactwith the real physical computer hardware 62.

FIG. 1C illustrates an alternative virtualized computing system whereinthe emulation is performed by a virtual machine monitor (VMM) 64′0running alongside the host operating system 64″. For certain embodimentsthe VMM 64′ may be an application running above the host operatingsystem 64″ and interacting with the physical computer hardware 62 onlythrough the host operating system 64″. In other embodiments, and asshown in FIG. 1C, the VMM 64′ may instead comprise a partiallyindependent software system that on some levels interacts indirectlywith the computer hardware 62 via the host operating system 64″ but onother levels the VMM 64′ interacts directly with the computer hardware62 (similar to the way the host operating system interacts directly withthe computer hardware). And in yet other embodiments, the VMM 64′ maycomprise a fully independent software system that on all levelsinteracts directly with the computer hardware 62 (similar to the way thehost operating system 64″ interacts directly with the computer hardware62) without utilizing the host operating system 64″ (although stillinteracting with said host operating system 64″ insofar as coordinatinguse of the computer hardware 62 and avoiding conflicts and the like).

All of these variations for implementing the virtual machine areanticipated to form alternative embodiments of the invention asdescribed herein, and nothing herein should be interpreted as limitingthe invention to any particular emulation embodiment. In addition, anyreference to interaction between applications 74, 76, and 78 via VM A 66and/or VM B 68 respectively (presumably in a hardware emulationscenario) should be interpreted to be in fact an interaction between theapplications 74, 76, and 78 and the virtualizer that has created thevirtualization. Likewise, any reference to interaction betweenapplications VM A 66 and/or VM B 68 with the host operating system 64and/or the computer hardware 62 (presumably to execute computerinstructions directly or indirectly on the computer hardware 62) shouldbe interpreted to be in fact an interaction between the virtualizer thathas created the virtualization and the host operating system 64 and/orthe computer hardware 62 as appropriate.

Virtual OS Device Communication Using Memory Access Violations

The present invention relates to features of a system that uses asoftware emulator to virtualize a legacy game system platform, such asXbox, on a host game system platform that is an upgrade of the legacygame system platform. The software emulator enables the host game systemplatform to run legacy games in a seamless fashion. As noted above, thepresent invention addresses the problems that occur when the drivers ofsuch legacy games attempt to access memory mapped I/O (MMIO) devicesthat are no longer present (or at least not present at the samelocation) in the host game system platform. The inventive solution tothese problems will be described below with respect to FIGS. 2-4.

In accordance with the invention, when the media loader of the host gamesystem console receives media containing a legacy computer game and isasked by the operating system of the host game system to boot the legacycomputer game, the media loader instead invokes a software emulator thatprovides backwards compatibility for the operation of the legacycomputer game. The software emulator loads and runs the legacy computergame as a standard game with the same rights and restrictions as anynative computer game of the host game system. At boot time, the softwareemulator requests that two physical memory chunks be reserved: a 64 MBsegment to host the virtualized legacy computer game, and a 64 MBsegment to provide a conduit between the virtual machine that implementsthe legacy computer game and host computer game system.

FIG. 2 illustrates the relationship between the virtual memory of thelegacy game system implemented in a virtual machine and the virtualmemory of the host game system. In this example, the legacy game systemis assumed to be Xbox, available from Microsoft Corporation. Asillustrated, the legacy Xbox game system is implemented in a virtualmachine environment and assumes a virtual address space 80 of 4 GB isavailable. As illustrated, the legacy 4 GB virtual address space isassumed by the legacy Xbox game system to have a section of memory 82dedicated to the virtual title of the inserted legacy game, a memory 84dedicated to the virtual legacy Kbox kernel, a 64 MB shared memory 86that maps directly to a 64 MB shared memory in a physical RAM 88 of thehost game system, and a virtual MMIO address space 90 in the upperregion of the 4 GB virtual address space. Those skilled in the art willappreciate that the MMIO address space 90 in the legacy Xbox game systemcontains pointers to the actual hardware devices that are called by thedrivers of the Xbox game system console's operating system. Inaccordance with the invention, the virtual address space accessed by thelegacy Xbox game as implemented in the virtual machine environment isconfigured the same as the virtual address space in the native legacyXbox game system environment, thus tricking the legacy Xbox game intothinking that it is operating in the native legacy Xbox game systemenvironment.

On the other hand, the virtual address space 92 of the native host Xboxgame system is characterized by an emulator binary memory 94, the nativehost Xbox kernel 96, and a 64 MB physical memory segment 98 that hoststhe legacy Xbox virtual machine. A 64 MB shared memory 100 is alsoprovided that maps directly to the 64 MB shared memory in the physicalRAM 88 of the native host Xbox game system. As will be explained in moredetail below with respect to FIG. 3, a recreated copy of the x86 Xboxkernel 84 as well as the x86 title binaries originally passed to thegame loader are loaded in the 64 MB space 98 reserved to the virtualXbox game system. In the 64 MB shared memory space 100, on the otherhand, the native host Xbox game system loads its dispatcher program,loads certain hand-optimized “glue” functions, and creates structuresfor virtual machine (VM) state and the translated code cache (FIG. 3).These functions are shared with the legacy Xbox game running on thevirtual machine via shared memory 88, which is actually a physicallyshared section of RAM accessible to both the virtual machineimplementing the legacy Xbox and the emulator engine of the native hostXbox operating system.

FIG. 3 illustrates a system in accordance with the invention forconverting attempts by the virtualized legacy game system to communicatewith hardware devices into the actual memory addresses of the hardwareof the native host game system. As illustrated, the backwardscompatibility system of the invention that implements this functionalityincludes four major components:

a just-in-time (JIT) binary translator 102 that provides just-in-timebinary translation of x86 code of the legacy Xbox game system to PPCcode or other processor code of the native host Xbox game system;

a legacy Xbox virtual machine (VM) 104 that recreates most of the legacyXbox environment in reproduced x86 Xbox kernel 106 and untranslatedtitle code store 108 and the legacy title environment in stored titleresources and state store 110;

a shared memory 88 that permits communication between the backwardscompatibility portion of the operating system of the native host Xboxgame system and the VM 104 and hosts the dispatcher 112 and thetranslated code cache 114 while tracking VM state 116; and

a hypervisor 128 and Xbox exception handler 118 that together provideexception handling while device emulation 120 further emulates thehardware devices of the native host Xbox system on the native Xboxkernel 122 for use by the Xbox VM 104 while running a legacy Xbox game.

As will be explained below, the system of the invention permits thelegacy Xbox game's device drivers to access the native host Xboxsystem's physical devices 124 by generating memory access violationsbased on attempts by the legacy Xbox game's device drivers to accessinvalid legacy Xbox MMIO device addresses at 126 and sending memoryaccess violations to hypervisor 128 for processing.

After initialization of a legacy Xbox game in the legacy Xbox virtualmachine 104, the operating system of the native host Xbox game systempasses control to the dispatcher 112, which resides in the shared memoryspace 88. Fundamentally, the dispatcher 112 directs code execution forthe virtualized legacy Xbox game. It maintains a mapping between everyx86 function referenced in the x86 space and an equivalent, translatedPPC (or other host processor) function in the translated code cache 114.The job of the dispatcher 112 is to chain translated PPC (or other hostprocessor) functions together in the sequence expected by thevirtualized x86 legacy Xbox title. The first task of dispatcher 112 isto simulate booting the legacy x86 Xbox kernel 106 and legacy x86 titlein title memory 110. If the host OS of the native host Xbox game systemperforms no significant pre-translation of emulated binaries, at firstthe dispatcher 112 has no cached PPC (or other host processor)equivalents for the requested x86 functions. To fill these gaps, thedispatcher 112 calls to the JIT binary translator 102 for just-in-timefunction translation.

Those skilled in the art will appreciate that translating x86 code toPPC code, for example, is problematic in some respects. For one thing,the x86 ISA contains several complex functions with no simple PPC ISAequivalents. For another, the PPC processor of the native host Xbox gamesystem is configured to interpret data as Big-Endian, whereas legacyXbox titles expect Little-Endian interpretation. In addition, naivetranslation of legacy Xbox x86 code can result in a huge magnificationof instructions and cache misses on the native host Xbox systemhardware. As explained in copending U.S. patent application Ser. No.______, to Tan, also assigned to the present assignee MicrosoftCorporation, the JIT binary translator 102 may be designed to take stepsto mitigate this “translation bloat.” The details regarding such JITtranslation techniques may be found in that patent application, thecontents of which are incorporated herein by reference.

After translation, the desired PPC function corresponding to the one ormore x86 instructions in the legacy Xbox command sequence executes,operating on resources within the 4 GB memory space of the legacy Xboxvirtual machine (104). When the legacy Xbox virtual machine completesprocessing of the desired PPC function, control jumps back to thedispatcher 112 by way of an interrupt with a request for the next x86function and the entire JIT binary translation cycle begins again. Sincecomputer games are generally coded as enormous loops, after the initialfew seconds of execution, most x86 functions have been translated andare present in the translated code cache 114 as optimized PPC code (orother processor code if the native host Xbox game system uses adifferent processor).

However, device requests and system calls by the legacy Xbox game arethe exceptions to this rule. The virtualized legacy Xbox game frequentlywants to speak to the legacy Xbox hardware but is unaware that it isoperating on the platform of the native host Xbox game system. As withmany operating systems, in the legacy Xbox operating system, gamescommunicated with most devices by writing to well-known Memory MappedI/O (MMIO) locations. As illustrated in FIG. 2, these MMIO locationswere, in the case of the Xbox operating system, in the upper region 90of the 4 GB virtual memory space. The present invention uses an accesscontrol list (ACL) to restrict and/or reduce page permissions (e.g., toread only or to no read or write) such that the virtual machine 104implementing the legacy Xbox game lacks read and write privileges tothese MMIO addresses in memory 90. As a result, when the legacy Xboxgame running in the virtual machine 104 attempts to access its expecteddevice memory 90, the host Xbox operating system detects invalid XboxMMIO device addresses at 126 and halts the thread. A memory accessviolation message is sent to the hypervisor 128 which, in turn, passesVM state information to the Xbox exception handler 118 to resolve thememory access violation.

The memory access violation and any intentional system calls forwardedto the Xbox exception handler 118 by the hypervisor 128 are processed todetermine the intended target device using the MMIO address provided inthe MMIO write from the legacy Xbox game. Since memory access violationsoften indicate a virtual device request, the Xbox exception handler 118may simply check the virtual machine state provided by the hypervisor128 (from VM state register 116) and determine the intended targetdevice. Control is then given to an appropriate Xbox device emulator 120in the Xbox exception handler 118, which translates and relays therequest of the virtual machine 104 to the appropriate functions of theXbox kernel 122 or to native host Xbox libraries. Since it cannot beassumed that the native host Xbox system shares any hardware with thelegacy Xbox system, simple instruction forwarding is not an option. Ofcourse, if hardware is shared, then instruction forwarding may be used.

As illustrated in FIG. 3, some native hardware requests to Xbox physicaldevices 124, such as hard drive I/O, produce asynchronous callbacks inthe form of device interrupts 130. When the native host Xbox kernel 122receives such an interrupt, it halts the JIT binary translator 102 andsupplies the interrupt data to an appropriate Xbox device emulator 120in the Xbox exception handler 118 that, in turn, translates the replyand stores it in the shared memory space 88. Control is then returned tothe virtual machine 104 by simulating a legacy Xbox interrupt so thatthe virtual machine 104 may handle the new data.

FIG. 4 illustrates a sample embodiment of the invention for enabling thevirtualized legacy Xbox game system to access integrated driveelectronics (IDE) controller hardware of the native host Xbox gamesystem in accordance with the invention. The virtual machine 104implementing the legacy Xbox game runs on the hypervisor 128 of thenative host Xbox machine 132. A virtual application (legacy game) 134makes a call to IDE controller hardware by making a standard API call tothe legacy hardware library 136. Legacy hardware library 136, in turn,calls the legacy IDE driver 138 typically provided from the mediacontaining the virtual application 134. The legacy IDE driver 138, inturn, writes to the MMIO addresses of the expected hardware. The writeto the virtual MMIO address fails since the page permissions to thevirtual MMIO addresses have been denied. As a result, a memory accessviolation is identified at 126 to the native operating system 140 of thenative Xbox machine 132. The memory access violation is provided to theemulator logic of the device emulator 120 of the Xbox exception handler118 of the native Xbox machine 132 for resolution. In turn, deviceemulator 120 calls the new hardware library 142 that, in turn, calls thenew hardware driver, which translates the MMIO address into thecorresponding commands to the new IDE driver 144. These commands arethen provided to the new IDE driver 144 of the native Xbox machine 132.The corresponding Xbox IDE physical device 124 is then accessed and theresulting data is accessed in a conventional manner. Those skilled inthe art will appreciated that, for certain hardware requests, such ashard drive I/O, device emulator 120 may produce an asynchronous callbackto virtual machine 104 in the form of a device interrupt.

Thus, the invention provides a mechanism whereby a program or gamerunning in a virtual machine environment may cause memory accessviolations to be generated when attempts are made to access legacyhardware that may no longer exist. The memory access violations are thenresolved by the host operating system in a conventional manner to obtainthe requested data that is, in turn, provided to the virtualized programor game that made the initial attempt to access legacy hardware. Thoseskilled in the art will appreciate that such techniques may be extendedto all sorts of applications, not just game systems. Moreover, thetechniques of the invention may be used to provide backwardscompatibility to other computer systems and game consoles that acceptapplication programs or computer games on inserted media.

Exemplary Networked and Distributed Environments

Although an exemplary embodiment of the invention may be implemented inconnection with the Xbox game system architecture, one of ordinary skillin the art can appreciate that the invention can be implemented inconnection with any suitable host computer or other client or serverdevice, which can be deployed as part of a computer network, or in adistributed computing environment. In this regard, the inventionpertains to any computer system or environment having any number ofmemory or storage units, and any number of applications and processesoccurring across any number of storage units or volumes, which may beused in connection with virtualizing a guest OS in accordance with theinvention. The invention may apply to an environment with servercomputers and client computers deployed in a network environment ordistributed computing environment, having remote or local storage. Theinvention may also be applied to standalone computing devices, havingprogramming language functionality, interpretation and executioncapabilities for generating, receiving and transmitting information inconnection with remote or local services.

Distributed computing provides sharing of computer resources andservices by exchange between computing devices and systems. Theseresources and services include the exchange of information, cachestorage and disk storage for files. Distributed computing takesadvantage of network connectivity, allowing clients to leverage theircollective power to benefit the entire enterprise. In this regard, avariety of devices may have applications, objects or resources that mayimplicate the processes of the invention.

FIG. 5A provides a schematic diagram of an exemplary networked ordistributed computing environment. The distributed computing environmentcomprises computing objects 145 a, 145 b, etc. and computing objects ordevices 146 a, 146 b, 146 c, etc. These objects may comprise programs,methods, data stores, programmable logic, etc. The objects may compriseportions of the same or different devices such as PDAs, audio/videodevices, MP3 players, personal computers, etc. Each object cancommunicate with another object by way of the communications network147. This network may itself comprise other computing objects andcomputing devices that provide services to the system of FIG. 5A, andmay itself represent multiple interconnected networks. In accordancewith an aspect of the invention, each object 145 a, 145 b, etc. or 146a, 146 b, 146 c, etc. may contain an application that might make use ofan API, or other object, software, firmware and/or hardware, to requestuse of the virtualization processes of the invention.

It can also be appreciated that an object, such as 146 c, may be hostedon another computing device 145 a, 145 b, etc. or 146 a, 146 b, etc.Thus, although the physical environment depicted may show the connecteddevices as computers, such illustration is merely exemplary and thephysical environment may alternatively be depicted or describedcomprising various digital devices such as PDAs, televisions, MP3players, etc., software objects such as interfaces, COM objects and thelike.

There are a variety of systems, components, and network configurationsthat support distributed computing environments. For example, computingsystems may be connected together by wired or wireless systems, by localnetworks or widely distributed networks. Currently, many of the networksare coupled to the Internet, which provides an infrastructure for widelydistributed computing and encompasses many different networks. Any ofthe infrastructures may be used for exemplary communications madeincident to the virtualization processes of the invention.

In home networking environments, there are at least four disparatenetwork transport media that may each support a unique protocol, such asPower line, data (both wireless and wired), voice (e.g., telephone) andentertainment media. Most home control devices such as light switchesand appliances may use power lines for connectivity. Data Services mayenter the home as broadband (e.g., either DSL or Cable modem) and areaccessible within the home using either wireless (e.g., HomeRF or802.11B) or wired (e.g., Home PNA, Cat 5, Ethernet, even power line)connectivity. Voice traffic may enter the home either as wired (e.g.,Cat 3) or wireless (e.g., cell phones) and may be distributed within thehome using Cat 3 wiring. Entertainment media, or other graphical data,may enter the home either through satellite or cable and is typicallydistributed in the home using coaxial cable. IEEE 1394 and DVI are alsodigital interconnects for clusters of media devices. All of thesenetwork environments and others that may emerge as protocol standardsmay be interconnected to form a network, such as an intranet, that maybe connected to the outside world by way of the Internet. In short, avariety of disparate sources exist for the storage and transmission ofdata, and consequently, moving forward, computing devices will requireways of sharing data, such as data accessed or utilized incident toprogram objects, which make use of the virtualized services inaccordance with the invention.

The Internet commonly refers to the collection of networks and gatewaysthat utilize the TCP/IP suite of protocols, which are well-known in theart of computer networking. TCP/IP is an acronym for “TransmissionControl Protocol/Internet Protocol.” The Internet can be described as asystem of geographically distributed remote computer networksinterconnected by computers executing networking protocols that allowusers to interact and share information over the network(s). Because ofsuch wide-spread information sharing, remote networks such as theInternet have thus far generally evolved into an open system for whichdevelopers can design software applications for performing specializedoperations or services, essentially without restriction.

Thus, the network infrastructure enables a host of network topologiessuch as client/server, peer-to-peer, or hybrid architectures. The“client” is a member of a class or group that uses the services ofanother class or group to which it is not related. Thus, in computing, aclient is a process, i.e., roughly a set of instructions or tasks, thatrequests a service provided by another program. The client processutilizes the requested service without having to “know” any workingdetails about the other program or the service itself. In aclient/server architecture, particularly a networked system, a client isusually a computer that accesses shared network resources provided byanother computer, e.g., a server. In the example of FIG. 5A, computers146 a, 146 b, etc. can be thought of as clients and computers 145 a, 145b, etc. can be thought of as the server where server 145 a, 145 b, etc.maintains the data that is then replicated in the client computers 146a, 146 b, etc., although any computer can be considered a client, aserver, or both, depending on the circumstances. Any of these computingdevices may be processing data or requesting services or tasks that mayimplicate an implementation of the virtualization processes of theinvention.

A server is typically a remote computer system accessible over a remoteor local network, such as the Internet. The client process may be activein a first computer system, and the server process may be active in asecond computer system, communicating with one another over acommunications medium, thus providing distributed functionality andallowing multiple clients to take advantage of the information-gatheringcapabilities of the server. Any software objects utilized pursuant tomaking use of the virtualized architecture(s) of the invention may bedistributed across multiple computing devices or objects.

Client(s) and server(s) communicate with one another utilizing thefunctionality provided by protocol layer(s). For example, HyperTextTransfer Protocol (HTTP) is a common protocol that is used inconjunction with the World Wide Web (WWW), or “the Web.” Typically, acomputer network address such as an Internet Protocol (IP) address orother reference such as a Universal Resource Locator (URL) can be usedto identify the server or client computers to each other. The networkaddress can be referred to as a URL address. Communication can beprovided over a communications medium, e.g., client(s) and server(s) maybe coupled to one another via TCP/IP connection(s) for high-capacitycommunication.

FIG. 5A illustrates an exemplary networked or distributed environment,with a server in communication with client computers via a network/bus,in which the invention may be employed. In more detail, a number ofservers 145 a, 145 b, etc., are interconnected via a communicationsnetwork/bus 147, which may be a LAN, WAN, intranet, the Internet, etc.,with a number of client or remote computing devices 146 a, 146 b, 146 c,146 d, 146 e, etc., such as a portable computer, handheld computer, thinclient, networked appliance, or other device, such as a VCR, TV, oven,light, heater and the like. It is thus contemplated that the inventionmay apply to any computing device in connection with which it isdesirable to implement guest interfaces and operating systems inaccordance with the invention.

In a network environment in which the communications network/bus 147 isthe Internet, for example, the servers 145 a, 145 b, etc. can be Webservers with which the clients 146 a, 146 b, 146 c, 146 d, 146 e, etc.communicate via any of a number of known protocols such as HTTP. Servers145 a, 145 b, etc. may also serve as clients 146 a, 146 b, 146 c, 146 d,146 e, etc., as may be characteristic of a distributed computingenvironment.

Communications may be wired or wireless, where appropriate. Clientdevices 146 a, 146 b, 146 c, 146 d, 146 e, etc. may or may notcommunicate via communications network/bus 147, and may have independentcommunications associated therewith. For example, in the case of a TV orVCR, there may or may not be a networked aspect to the control thereofEach client computer 146 a, 146 b, 146 c, 146 d, 146 e, etc. and servercomputer 145 a, 145 b, etc. may be equipped with various applicationprogram modules or objects 148 and with connections or access to varioustypes of storage elements or objects, across which files or data streamsmay be stored or to which portion(s) of files or data streams may bedownloaded, transmitted or migrated. Any one or more of computers 145 a,145 b, 146 a, 146 b, etc. may be responsible for the maintenance andupdating of a database 149 or other storage element, such as a databaseor memory 149 for storing data processed according to the invention.Thus, the invention can be utilized in a computer network environmenthaving client computers 146 a, 146 b, etc. that can access and interactwith a computer network/bus 147 and server computers 145 a, 145 b, etc.that may interact with client computers 146 a, 146 b, etc. and otherlike devices, and databases 149.

Exemplary Computing Device

FIG. 5B and the following discussion are intended to provide a briefgeneral description of a suitable host computing environment inconnection with which the invention may be implemented. It should beunderstood, however, that handheld, portable and other computingdevices, portable and fixed gaming devices, and computing objects of allkinds are contemplated for use in connection with the invention. While ageneral purpose computer is described below, this is but one example,and the invention may be implemented with a thin client havingnetwork/bus interoperability and interaction. Thus, the invention may beimplemented in an environment of networked hosted services in which verylittle or minimal client resources are implicated, e.g., a networkedenvironment in which the client device serves merely as an interface tothe network/bus, such as an object placed in an appliance. In essence,anywhere that data may be stored or from which data may be retrieved ortransmitted to another computer is a desirable, or suitable, environmentfor operation of the virtualization techniques in accordance with theinvention.

Although not required, the invention can be implemented in whole or inpart via an operating system, for use by a developer of services for adevice or object, and/or included within application software thatoperates in connection with the virtualized OS of the invention.Software may be described in the general context of computer-executableinstructions, such as program modules, being executed by one or morecomputers, such as client workstations, servers or other devices.Generally, program modules include routines, programs, objects,components, data structures and the like that perform particular tasksor implement particular abstract data types. Typically, thefunctionality of the program modules may be combined or distributed asdesired in various embodiments. Moreover, those skilled in the art willappreciate that the invention may be practiced with other computersystem configurations and protocols. Other well known computing systems,environments, and/or configurations that may be suitable for use withthe invention include, but are not limited to, personal computers (PCs),automated teller machines, server computers, hand-held or laptopdevices, multi-processor systems, microprocessor-based systems,programmable consumer electronics, network PCs, appliances, lights,environmental control elements, minicomputers, mainframe computers andthe like. As noted above, the invention may also be practiced indistributed computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network/busor other data transmission medium. In a distributed computingenvironment, program modules may be located in both local and remotecomputer storage media including memory storage devices, and clientnodes may in turn behave as server nodes.

FIG. 5B illustrates an example of a suitable host computing systemenvironment 150 in which the invention may be implemented, although asmade clear above, the host computing system environment 150 is only oneexample of a suitable computing environment and is not intended tosuggest any limitation as to the scope of use or functionality of theinvention. Neither should the computing environment 150 be interpretedas having any dependency or requirement relating to any one orcombination of components illustrated in the exemplary operatingenvironment 150.

With reference to FIG. 5B, an exemplary system for implementing theinvention includes a general purpose computing device in the form of acomputer 160. Components of computer 160 may include, but are notlimited to, a processing unit 162, a system memory 164, and a system bus166 that couples various system components including the system memoryto the processing unit 162. The system bus 166 may be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Association (VESA) local bus, Peripheral ComponentInterconnect (PCI) bus (also known as Mezzanine bus), and PCI Express(PCIe).

Computer 160 typically includes a variety of computer readable media.Computer readable media can be any available media that can be accessedby computer 160 and includes both volatile and nonvolatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes both volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CDROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can be accessed by computer 160. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier waveor other transport mechanism and includes any information deliverymedia. The term “modulated data signal” means a signal that has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, RF,infrared and other wireless media. Combinations of any of the aboveshould also be included within the scope of computer readable media.

The system memory 164 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 168and random access memory (RAM) 170. A basic input/output system 172(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 160, such as during start-up, istypically stored in ROM 168. RAM 170 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 162. By way of example, and notlimitation, FIG. 5B illustrates operating system 174, applicationprograms 176, other program modules 178, and program data 180.

The computer 160 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 5B illustrates a hard disk drive 182 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 184that reads from or writes to a removable, nonvolatile magnetic disk 186,and an optical disk drive 188 that reads from or writes to a removable,nonvolatile optical disk 190, such as a CD-ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM and the like. The hard disk drive 182 is typically connectedto the system bus 166 through a non-removable memory interface such asinterface 192, and magnetic disk drive 184 and optical disk drive 188are typically connected to the system bus 166 by a removable memoryinterface, such as interface 194.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 5B provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 160. In FIG. 5B, for example, hard disk drive 182 isillustrated as storing operating system 196, application programs 198,other program modules 200 and program data 202. Note that thesecomponents can either be the same as or different from operating system174, application programs 176, other program modules 178 and programdata 180. Operating system 196, application programs 198, other programmodules 200 and program data 202 are given different numbers here toillustrate that, at a minimum, they are different copies. A user mayenter commands and information into the computer 160 through inputdevices such as a keyboard 204 and pointing device 206, commonlyreferred to as a mouse, trackball or touch pad. Other input devices (notshown) may include a microphone, joystick, game pad, satellite dish,scanner, or the like. These and other input devices are often connectedto the processing unit 162 through a user input interface 208 that iscoupled to the system bus 166, but may be connected by other interfaceand bus structures, such as a parallel port, game port or a universalserial bus (USB). These are the kinds of structures that are virtualizedby the architectures of the invention. A graphics interface 210, such asone of the interfaces implemented by the Northbridge, may also beconnected to the system bus 166. Northbridge is a chipset thatcommunicates with the CPU, or host processing unit 162, and assumesresponsibility for communications such as PCI, PCIe and acceleratedgraphics port (AGP) communications. One or more graphics processingunits (GPUs) 212 may communicate with graphics interface 210. In thisregard, GPUs 212 generally include on-chip memory storage, such asregister storage and GPUs 212 communicate with a video memory 214. GPUs212, however, are but one example of a coprocessor and thus a variety ofcoprocessing devices may be included in computer 160, and may include avariety of procedural shaders, such as pixel and vertex shaders. Amonitor 216 or other type of display device is also connected to thesystem bus 166 via an interface, such as a video interface 218, whichmay in turn communicate with video memory 214. In addition to monitor216, computers may also include other peripheral output devices such asspeakers 220 and printer 222, which may be connected through an outputperipheral interface 224.

The computer 160 may operate in a networked or distributed environmentusing logical connections to one or more remote computers, such as aremote computer 226. The remote computer 226 may be a personal computer,a server, a router, a network PC, a peer device or other common networknode, and typically includes many or all of the elements described aboverelative to the computer 160, although only a memory storage device 228has been illustrated in FIG. 5B. The logical connections depicted inFIG. 5B include a local area network (LAN) 230 and a wide area network(WAN) 232, but may also include other networks/buses. Such networkingenvironments are commonplace in homes, offices, enterprise-wide computernetworks, intranets and the Internet.

When used in a LAN networking environment, the computer 160 is connectedto the LAN 230 through a network interface or adapter 234. When used ina WAN networking environment, the computer 160 typically includes amodem 236 or other means for establishing communications over the WAN232, such as the Internet. The modem 236, which may be internal orexternal, may be connected to the system bus 166 via the user inputinterface 208, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 160, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 5B illustrates remoteapplication programs 238 as residing on memory device 228. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

There are multiple ways of implementing the invention, e.g., anappropriate API, tool kit, driver code, operating system, control,standalone or downloadable software object, etc. which enablesapplications and services to use the virtualized architecture(s),systems and methods of the invention. The invention contemplates the useof the invention from the standpoint of an API (or other softwareobject), as well as from a software or hardware object that receives anyof the aforementioned techniques in accordance with the invention. Thus,various implementations of the invention described herein may haveaspects that are wholly in hardware, partly in hardware and partly insoftware, as well as in software.

As mentioned above, while exemplary embodiments of the invention havebeen described in connection with various computing devices and networkarchitectures, the underlying concepts may be applied to any computingdevice or system in which it is desirable to emulate guest software. Forinstance, the various algorithm(s) and hardware implementations of theinvention may be applied to the operating system of a computing device,provided as a separate object on the device, as part of another object,as a reusable control, as a downloadable object from a server, as a“middle man” between a device or object and the network, as adistributed object, as hardware, in memory, a combination of any of theforegoing, etc. One of ordinary skill in the art will appreciate thatthere are numerous ways of providing object code and nomenclature thatachieves the same, similar or equivalent functionality achieved by thevarious embodiments of the invention.

As mentioned, the various techniques described herein may be implementedin connection with hardware or software or, where appropriate, with acombination of both. Thus, the methods and apparatus of the invention,or certain aspects or portions thereof, may take the form of programcode (i.e., instructions) embodied in tangible media, such as floppydiskettes, CD-ROMs, hard drives, or any other machine-readable storagemedium, wherein, when the program code is loaded into and executed by amachine, such as a computer, the machine becomes an apparatus forpracticing the invention. In the case of program code execution onprogrammable computers, the computing device generally includes aprocessor, a storage medium readable by the processor (includingvolatile and non-volatile memory and/or storage elements), at least oneinput device, and at least one output device. One or more programs thatmay implement or utilize the virtualization techniques of the invention,e.g., through the use of a data processing API, reusable controls, orthe like, are preferably implemented in a high level procedural orobject oriented programming language to communicate with a computersystem. However, the program(s) can be implemented in assembly ormachine language, if desired. In any case, the language may be acompiled or interpreted language, and combined with hardwareimplementations.

The methods and apparatus of the invention may also be practiced viacommunications embodied in the form of program code that is transmittedover some transmission medium, such as over electrical wiring orcabling, through fiber optics, or via any other form of transmission,wherein, when the program code is received and loaded into and executedby a machine, such as an EPROM, a gate array, a programmable logicdevice (PLD), a client computer, etc., the machine becomes an apparatusfor practicing the invention. When implemented on a general-purposeprocessor, the program code combines with the processor to provide aunique apparatus that operates to invoke the functionality of theinvention. Additionally, any storage techniques used in connection withthe invention may invariably be a combination of hardware and software.

While the invention has been described in connection with the preferredembodiments of the various figures, it is to be understood that othersimilar embodiments may be used or modifications and additions may bemade to the described embodiment for performing the same function of theinvention without deviating therefrom. For example, while exemplarynetwork environments of the invention are described in the context of anetworked environment, such as a peer to peer networked environment, oneskilled in the art will recognize that the invention is not limitedthereto, and that the methods, as described in the present applicationmay apply to any computing device or environment, such as a gamingconsole, handheld computer, portable computer, etc., whether wired orwireless, and may be applied to any number of such computing devicesconnected via a communications network, and interacting across thenetwork. Furthermore, it should be emphasized that a variety of computerplatforms, including handheld device operating systems and otherapplication specific operating systems are contemplated, especially asthe number of wireless networked devices continues to proliferate.

While exemplary embodiments refer to utilizing the invention in thecontext of a guest OS virtualized on a host OS, the invention is not solimited, but rather may be implemented to virtualize a secondspecialized processing unit cooperating with a main processor for otherreasons as well. Moreover, the invention contemplates the scenariowherein multiple instances of the same version or release of an OS areoperating in separate virtual machines according to the invention. Itcan be appreciated that the virtualization of the invention isindependent of the operations for which the guest OS is used. It is alsointended that the invention applies to all computer architectures, notjust the Windows or Xbox architecture. Still further, the invention maybe implemented in or across a plurality of processing chips or devices,and storage may similarly be effected across a plurality of devices.Therefore, the invention should not be limited to any single embodiment,but rather should be construed in breadth and scope in accordance withthe appended claims.

1. A method of enabling an application program executing on avirtualized legacy computer system to access physical hardware of a hostcomputer system, comprising: when an attempt is made by said applicationprogram to access hardware of said virtualized legacy computer system,generating a memory access violation; providing to an emulation deviceof said host computer system information identifying at least thehardware of said virtualized legacy computer system that saidapplication program attempted to access; and said emulation device ofsaid host computer system emulating the hardware of the virtualizedlegacy computer system to effect the activity expected by saidapplication program in response to the requested hardware access of saidvirtualized legacy computer system.
 2. A method as in claim 1, whereinsaid application program is a computer game.
 3. A method as in claim 2,wherein said hardware of said virtualized legacy computer system ismemory mapped and said attempt by said computer game to access saidhardware of said virtualized legacy computer system comprises generatinga write to a memory mapped address for the desired hardware component ofsaid virtualized legacy computer system.
 4. A method as in claim 3,further comprising the step of denying access to said memory mappedaddress for the desired hardware component of said virtualized legacycomputer system.
 5. A method as in claim 4, wherein access to saidmemory mapped address for the desired hardware component of saidvirtualized legacy computer system is denied by denying write and/orread/write permission by said computer game to the memory mapped addressof the desired hardware component of said virtualized legacy computersystem.
 6. A method as in claim 4, wherein access to said memory mappedaddress for the desired hardware component of said virtualized legacycomputer system is denied by reducing page permissions for saidapplication program to said memory mapped address.
 7. A method as inclaim 1, wherein said emulating step comprises the steps of using saidinformation identifying said hardware of said virtualized legacycomputer system to determine which hardware of said host computer systemcorresponds to said hardware of said virtualized legacy computer systemand generating commands to said hardware of said host computer systemthat correspond to commands generated by said application program foraccessing the hardware of said virtualized legacy computer system.
 8. Amethod as in claim 1, wherein said virtualized legacy computer systemand said emulation device communicate via a shared memory of said hostcomputer system
 9. A system that enables an application programexecuting on a virtualized legacy computer system to access physicalhardware of a host computer system, comprising: a virtual machine systemthat virtualizes said legacy computer system and executes saidapplication program on said virtualized legacy computer system, saidvirtual machine system generating a memory access violation when anattempt is made by said application program to access hardware of saidvirtualized legacy computer system, said memory access violationincluding information identifying at least the hardware of saidvirtualized legacy computer system that said application programattempted to access; and an emulation device that uses said informationto emulate the hardware of the virtualized legacy computer system toeffect the activity expected by said application program in response tothe requested hardware access of said virtualized legacy computersystem.
 10. A system as in claim 9, wherein said application program isa computer game and said legacy computer system and said host computersystem and computer game systems.
 11. A system as in claim 10, whereinsaid hardware of said virtualized legacy computer system is memorymapped and said computer game accesses said hardware of said virtualizedlegacy computer system by generating a write to a memory mapped addressfor the desired hardware component of said virtualized legacy computersystem.
 12. A system as in claim 11, wherein said virtual machine isconfigured to deny access by said computer game to said memory mappedaddress for the desired hardware component of said virtualized legacycomputer system.
 13. A system as in claim 12, wherein said virtualmachine denies access to said memory mapped address of the desiredhardware component of said virtualized legacy computer system by denyingwrite and/or read/write permission by said computer game to the memorymapped address of the desired hardware component of said virtualizedlegacy computer system.
 14. A system as in claim 12, wherein saidvirtual machine denies access to said memory mapped address of thedesired hardware component of said virtualized legacy computer system byreducing page permissions for said application program to said memorymapped address of the desired hardware component of said virtualizedlegacy computer system.
 15. A system as in claim 9, wherein saidemulation device uses said information identifying said hardware of saidvirtualized legacy computer system to determine which hardware of saidhost computer system corresponds to said hardware of said virtualizedlegacy computer system and generates commands to said hardware of saidhost computer system that correspond to commands generated by saidapplication program for accessing the hardware of said virtualizedlegacy computer system.
 16. A system as in claim 9, further comprising ashared memory of said host system that said virtual machine and saidemulation device use to communicate with each other.
 17. A computerreadable medium that when inserted into a host computer system creates aprocessing system that enables an application program executing on avirtualized legacy computer system to access physical hardware of saidhost computer system, comprising: virtual machine system software thatvirtualizes said legacy computer system and executes said applicationprogram on said virtualized legacy computer system, said virtual machinesystem software generating a memory access violation when an attempt ismade by said application program to access hardware of said virtualizedlegacy computer system, said memory access violation includinginformation identifying at least the hardware of said virtualized legacycomputer system that said application program attempted to access; andemulation software that uses said information to emulate the hardware ofthe virtualized legacy computer system to effect the activity expectedby said application program in response to the requested hardware accessof said virtualized legacy computer system.
 18. A computer readablemedium as in claim 17, wherein said hardware of said virtualized legacycomputer system is memory mapped and said virtual machine softwaregenerates said memory access violation when said application programattempts to write a memory mapped address for the desired hardwarecomponent of said virtualized legacy computer system.
 19. A computerreadable medium as in claim 17, wherein said emulation software usessaid information identifying said hardware of said virtualized legacycomputer system to determine which hardware of said host computer systemcorresponds to said hardware of said virtualized legacy computer systemand generates commands to said hardware of said host computer systemthat correspond to commands generated by said application program foraccessing the hardware of said virtualized legacy computer system.
 20. Acomputer readable medium as in claim 17, wherein said virtual machinesoftware and said emulation software each comprise software that enablesaid virtual machine software and said emulation software to communicatewith each other via a shared memory of said host computer system.